Foodborne, commonly called food poisoning, and waterborne illnesses are conditions caused by eating or drinking food or water that is contaminated by microbes or the toxins they produce. They typically cause gastrointestinal symptoms such as abdominal pain, nausea, vomiting, and diarrhea. There are many non-infectious causes of illness from contaminated food and water, and some microbes can lead to infections other than in the digestive tract, but these are beyond the scope of this article and are not covered here.

In the United States, the Centers for Disease Control and Prevention (CDC) estimates that as many as 1 in 6 people get sick each year from consuming contaminated food or beverages. Of those, roughly 128,000 are hospitalized and as many as 3,000 die from complications.

Foodborne and waterborne illnesses can affect anyone at any time but tend to be the most severe in:

Very young children and the elderly, who may experience serious dehydration

People with weakened (compromised) immune systems such as those with HIV/AIDS or who have had an organ transplant; in these populations, the conditions may be much more severe and difficult to resolve.

These illnesses, commonly called food poisoning, may involve single individuals or may be part of an outbreak. Most cases come directly from what is consumed. Sometimes they may be passed from person to person, especially in confined populations such as may be seen in a daycares, cruise ships, or nursing homes.

Outbreaks occur when more than one individual develops symptoms after consuming the same food or drink that is contaminated with the same microbe or toxin. They can be within the same local area or may occur across several states. Public health and government agencies continuously monitor food and water quality and take prompt actions to identify, contain, and correct sources of outbreaks. This job has become more complex as food is imported to the U.S. from many countries and as more people travel worldwide.

When cases of suspected food poisoning may be related, public health professionals endeavor to get complete medical histories of the people who are affected and obtain samples, usually stool, to send to public health laboratories for testing. Patients can be helpful in this process by sharing information with their healthcare practitioners on symptoms, type of diarrhea (watery, bloody), recent travel as well as food recently eaten. Sometimes it is useful to write down what was eaten in the last ten days or so. These details may help provide clues as to the cause of illness.

Often, samples of the suspected source of contamination are also tested. Public health laboratories use a molecular test called pulsed-field gel electrophoresis (PFGE) that "fingerprints" DNA to compare the microbe isolated from people who are ill and then look for the pathogens in food or water samples. This allows the laboratories to rapidly identify common sources of food or waterborne illness. The results from this testing are entered into a database called PulseNet. The database is used by local and state public health agencies, federal food safety regulatory laboratories, and the CDC to compare DNA fingerprints and quickly identify illnesses that have a common source. If one is identified, steps are taken to contain the source of the contamination and limit spread of the illness.

Food Contamination
Food may become contaminated at any point in its growth, processing, storage, and handling. Examples of contamination sources include:

Plants may be contaminated by soil, animal waste fertilizers, or water. If contaminated water is used to water or wash produce such as spinach or lettuce, for instance, then the fresh produce may become contaminated.

Animals may be colonized by bacteria that do not make them ill but that can make people sick. Salmonella, for instance, are bacteria that are common in poultry. They can be present even inside intact eggs and can make a person ill if the food is not fully cooked.

Intestinal bacteria may contaminate meat, such as beef, during processing. If the beef is then ground, the contamination can spread throughout the hamburger produced and, if the meat is not adequately cooked, it can cause illness.

Foods such as raw oysters or alfalfa sprouts may become contaminated while maturing and, when eaten raw, they can make a person sick.

Workers in the food industry and people in their own homes who do not use sanitary techniques can spread and transfer contamination. For instance, a cutting board that is used to cut contaminated meat and then used to chop produce without being thoroughly cleaned first can spread contamination to the produce. Also, someone who is sick can pass the illness to others during food preparation.

Milk and juices that are unpasteurized can be a source of bacterial foodborne illness. Some bacteria, such as Listeria, can grow even when milk is refrigerated.

Food that is left out too long, such as at a picnic, may allow the growth of bacteria.

Some bacteria and plants produce toxins that can cause foodborne illness. Examples of these are the muscle-paralyzing botulism caused by the toxin produced by Clostridium botulinum bacteria and the toxin produced by Staphylcoccus aureus. Some toxins are destroyed by cooking, others are not.

Other toxins and poisons that can contaminate food, such as pesticides and heavy metals such as mercury and lead, or that occur naturally in foods, such as in poisonous mushrooms, can also cause illness but are outside the scope of this article.

Water Contamination
People get waterborne illnesses primarily by drinking contaminated water, including treated drinking water, well water, water that is used to irrigate crops, and recreational water such as that found in lakes, rivers, and swimming pools as well as some temperate ocean waters. Even ice cubes or the small amounts of water swallowed during swimming can cause illness. When contaminated water is used for washing food, dishes, or surfaces, the contamination can be spread.

The contaminating microbes may naturally live in the environment or may get into the water from animal or human feces. Many parasites are hardy and can live in a dormant stage in soil or water for extended periods of time. Water can also become contaminated during natural disasters, such as hurricanes and earthquakes. Anything that adds wastes, sewage, or other health hazards into the water supply and disrupts the availability of treated drinking water has the potential to make people sick.

The microbes that can contaminate food and water include a wide range of bacteria, viruses, and parasites. Some are found throughout the world while others are regional. Some are very common, others more rare. They may cause symptoms in most people who are exposed to them or only in those who are most susceptible. Regional strains of bacteria may not cause symptoms in the people who are accustomed to them but may make visitors sick. Though the affected water and food may smell, look, and taste normal, they can cause illness ranging from mild and self-limited to severe.

Norovirus is the leading cause of food and waterborne illnesses, according to the most recent numbers from the Centers for Disease Control and Prevention (CDC). It is a very contagious virus that can contaminate food and water and also be spread from person to person.

Norovirus, Salmonella, Listeria, and the parasite Toxoplasma are also considered to be among the most common causes of death due to foodborne illness. Norovirus usually causes only a mild illness, but because it affects so many people, it is among the top causes of death.

Select one of the links below to read the details about these and other microbes that have been implicated in food and waterborne illnesses:

(Note: There are many other non-infectious causes of illness from consuming food or drink, such as poisoning from fish contaminated with toxins, but these are beyond the scope of this article.)

Bacteria

Salmonella—these bacteria may contaminate raw meat, poultry eggs, and other foods. Symptoms usually develop within 12 to 72 hours after infection and can last from 4 to 7 days. The infection usually resolves without treatment or with supportive care only, but in some people, such as the very young or elderly, the diarrhea may become so severe that they require hospitalization. In those that are very ill, there is a danger that the infection may spread to the blood, and there is a risk of death. These severe cases must be treated promptly with antibiotics. Salmonellaserotype Enteritidis and Salmonella serotype Typhimurium are common in the U.S. Many cases are travel-related. Salmonella typhi, which is common in developing countries, causes typhoid fever.

Campylobacter are relatively common bacteria. Campylobacter jejuni has been implicated in some recent outbreaks. Illnesses causing watery and/or blood stools may develop 2 to 5 days after infection and last about a week; they are usually seen with unpasteurized milk or cheese, raw or undercooked poultry, or contaminated water. Complications from the infection include Guillain-Barré syndrome and reactive arthritis. The number of cases is typically increased in spring and fall. Usually, supportive care is sufficient treatment, but some severe or prolonged cases may require antibiotics.

Escherichia coli—E. coli are common bacteria normally found in the digestive tract of humans and animals. Most strains don't cause problems, but some produce a toxin, known as the "shiga toxin," that can cause bloody diarrhea and potentially serious infections spread from sources such as undercooked meat or from person to person. These are known as shiga toxin-producing E coli or STEC. One particularly severe strain that has been implicated in several outbreaks is designated as O157:H7. The very young and the elderly are usually the most severely affected by complications of STEC infections, such a hemolytic uremic syndrome (HUS).

Listeria monocytogenes—found in uncooked meats, vegetables, fruits, soft cheeses, hot dogs, and unpasteurized milk. These bacteria can grow well even at refrigerator temperatures. The illness can be serious in those with weakened immune systems and can be passed from a pregnant woman to her developing baby and cause miscarriage.

Vibrio—found in contaminated seafood such as raw oysters. Vibrio parahaemolyticus is the most common; Vibrio vulnificus is found in warm seawater and can be deadly, especially in those with liver disease or weakened immune systems. Vibrio cholerae is responsible for cholera.

Yersinia—found in undercooked pork, seafood, and unpasteurized milk; it is frequently associated with 'chitlins,' a dish prepared from intestines of hogs often served during holidays, leading to an increased number of cases in winter. The infection is associated with reactive arthritis. Yersinia enterocolitica is the most common species.

Norovirus (Norwalk-like virus)—the most common cause of gastroenteritis in the U.S., causing over 50% of foodborne illnesses. It is resistant to disinfectants and is very contagious as it can be spread from person to person, by contaminated food or water, or by touching contaminated surfaces. It is a common cause of illness on cruise ships, in restaurants, and other confined populations. Most people get better in about 1 to 3 days, but there is a risk of dehydration and serious illness in young children, the elderly, and people with underlying conditions. People with severe dehydration may need to be hospitalized; antibiotics are NOT used for treatment since it is a virus, not a bacterium.

Rotavirus—very common in children; it can cause severe diarrhea and dehydration in this population and in the immunocompromised.

Hepatitis A—the number of cases in the U.S. is decreasing, but the infection is prevalent in other parts of the world; infection can be acquired from sewage-contaminated water, shellfish, and/or vegetables and other uncooked foods. A vaccine is available to prevent infection.

Parasites

Common parasites causing food and waterborne illness include:

Toxoplasma gondii—this is a single-celled parasite that can be ingested when consuming contaminated food or water, especially undercooked pork, lamb or venison; it may also be acquired by handling contaminated cat litter, by transmission from a pregnant woman to her developing baby, and rarely may be transmitted during an organ transplantation or blood transfusion. Most healthy people who become infected are not aware of it, and if symptoms are present, they are usually mild and flu-like. Their immune systems are able to protect them against more severe forms of infection. People with weakened immune systems and infants born to mothers who become infected with the parasite during or just before pregnancy are most vulnerable to serious infection.

Giardia duodenalis (Giardia intestinalis, Giardia lamblia)—a very common cause of waterborne illness, it also can contaminate food and may be passed from person to person; an infected person may have few and/or intermittent symptoms.

Entamoeba histolytica— a parasite acquired from contaminated water or food; it can be spread from person to person.

Cryptosporidium parvum—also called "crypto," may be found in food and water; infection can be severe and persistent in the immunocompromised.

Microsporidia, multiple species—infection from contaminated water can cause chronic diarrhea in immunocompromised people.

Cystoisospora belli—found in contaminated water and food; most common in tropical areas

Trichinella spiralis—causes trichinosis; rare in U.S. now but may be seen with undercooked pork and wild game; cysts of the parasite can lodge in muscles

Taenia solium and Taenia saginata—pork and beef tapeworms from raw or undercooked meat, contaminated food or water

Toxins

Other sources of food and waterborne illnesses include toxins that are produced by some bacteria. They may include:

Staphylococcus aureus—can produce a toxin that causes acute symptoms of nausea and vomiting within several hours of consuming the contaminated food

Clostridium perfringens—these bacteria may contaminate raw meat and poultry; disease is associated with food that is not cooked, heated or stored properly. The bacteria form spores that resist high temperatures, so when food that has been cooked cools down, the bacteria can begin to grow. The ingested bacteria produce a toxin that causes an acute infection, with symptoms of intestinal cramping and diarrhea (but no fever or vomiting) that typically develop within 8 to 12 hours, lasting less than 24 hours. As with other causes of food and waterborne illnesses, the infection can become serious in those who are most vulnerable.

Clostridium botulinum—from contaminated food, toxin can cause paralysis and can be fatal. Illness can be seen with low acid home-canned food; toxin is destroyed by high temperatures.

Bacteria and viruses tend to cause acute illness while parasites are more likely to cause chronic and/or intermittent illness. Each type of illness has its own incubation period, from several hours to days after consuming contaminated food or water, and length of illness from days to weeks.

A diagnosis of a food or waterborne illness may be initially made clinically by documenting a person's signs and symptoms, their severity and duration, what the person has consumed before the symptoms began, and where the person may have traveled.

Many food and waterborne illnesses caused by bacteria and viruses tend to be self-limiting. Because of this, testing may not be performed unless symptoms:

Are thought to be caused by a different condition with similar symptoms

Testing may be performed on those affected to diagnose a condition and sometimes to monitor the effectiveness of treatment.

Laboratory testing on samples of the food or water that are suspected of causing illness may be performed to help determine the source of contamination, especially with outbreaks. In these cases, testing of both people and food and water may be performed at the state, national, or international public health level to determine which strains of microbes are causing illness, to monitor their locations, and to manage and contain outbreaks.

Initial testing for an individual suspected of having a food or waterborne illness often begins with an examination of stool. This may include one or more of the following:

Antibody testing on a blood sample for specific bacteria or for hepatitis A; occasionally ordered to help confirm a diagnosis

In addition, specific nutrient media for culture and special techniques may be needed to detect and identify some microbes. The healthcare practitioner must recognize potential exposures and request specialized testing.

Public health laboratory testing

Healthcare practitioners and clinical laboratories report suspected cases of foodborne illness to local or state public health agencies and investigations are undertaken to identify the likely source of the illnesses. Stool samples from affected people and/or samples of the microbe causing the illnesses are often sent to public health laboratories so that special testing can be done. If bacteria are suspected to be the cause, these labs can perform molecular tests that can determine a "DNA fingerprint," also known as a pulsed field gel electrophoresis (PFGE) pattern, of the pathogen that is present.

This information is entered into PulseNet, a database used by local and state public health agencies, federal food safety regulatory labs, and the Centers for Disease Control and Prevention (CDC) to track illnesses. It allows for rapid comparison of DNA fingerprints in order to determine if illnesses and groups of illnesses are related. PulseNet also has an international component that allows for tracking of illnesses that may cross borders, an important activity given the increasing globalization of the food supply.

Most bacterial and viral water and foodborne illnesses are self-limited and do not require anything but supportive care that includes fluid replacement and rest. Over the counter diarrhea medications are often not recommended as they can prolong the duration of symptoms. Careful hygiene is important so that the contamination is contained.

In cases involving severe symptoms and significant dehydration, intravenous fluids and hospitalization may be required. With some cases, there is a risk that the infection may spread to the blood and other organs of the body. If the illness is caused by bacteria, treatment with antibiotics may be necessary. Infants, young children, the elderly and people with weakened immune systems, such as those with HIV/AIDS or organ transplant recipients, are most at risk of serious disease.

There are several steps that can be taken to prevent food and waterborne illnesses on an individual level. Some of these include:

Using care to contain sources of contamination and cross-contamination, such as raw meat, poultry or seafood, in the home during food preparation

Washing hands thoroughly with soap and water before preparing food or eating, after using the toilet, caring for people with diarrhea or touching or petting animals (when water is not available, alcohol-based hand sanitizers with at least 60% alcohol are an acceptable alternative)

Cooking meats to established safe temperatures

Storing foods at safe temperatures and for safe storage times

Not drinking untreated water or unpasteurized milk or juices

Being aware of food and beverage hazards while traveling

Being especially careful when a person is immunocompromised, has an underlying health condition, or is pregnant

Monitoring the production of food and ensuring good health practices are followed

Ensuring accurate and timely surveillance, response and support for local as well as multi-state outbreaks of foodborne illness

There are vaccines available to prevent some of the causes of foodborne and waterborne illnesses. Some examples include rotavirus infection and hepatitis A infection. Rotavirus and hepatitis A vaccines may be given routinely to children, and hepatitis A vaccination may be recommended for some adults who are traveling internationally.

Foodsafety.gov. Food Poisoning. Available online at https://www.foodsafety.gov/poisoning/. Accessed April 2017.

(September 24, 2015) Centers for Disease Control and Prevention. Food Safety, Foodborne Germs and Illnesses. Available online at https://www.cdc.gov/foodsafety/foodborne-germs.html. Accessed April 2017.

(March 24, 2015) United States Department of Agriculture Food Safety and Inspection Service. Foodborne Illness and Disease. Available online at https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/foodborne-illness-and-disease/foodborne-illness-and-disease. Accessed April 2017.

(April 16, 2004) Center for Disease Control and Prevention. Diagnosis and Management of Foodborne Illnesses. MMWR. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5304a1.htm. Accessed May 2012.